3/1/2015
Feasibility and
Potential Design of
a Renewable OffGrid Eco-Gym
Thomas Robinson - Andrew Lewis - Mustafa Mangel
Sarah Jackson - Benarsh Laly
GROUP 9
Page |1
Contents
Executive Summary ..................................................................................................................................................1
1.1 Introduction ........................................................................................................................................................2
2.1 Brief ....................................................................................................................................................................2
3.1 Eco gym energy consumption ............................................................................................................................2
3.2 Swimming Pool ...................................................................................................................................................2
3.3 Lighting ...............................................................................................................................................................3
3.3 Heating ...............................................................................................................................................................4
3.4 Air-conditioning ..................................................................................................................................................5
3.5 Miscellaneous .....................................................................................................................................................5
3.6 Gym Equipment ..................................................................................................................................................5
3.7 Total Power Consumption ..................................................................................................................................5
..................................................................................................................................................................................6
4.1 Possible Sources of Renewable Energy ..............................................................................................................6
4.2 Solar Cells........................................................................................................................................................6
4.3 Transparent Solar Cells ...................................................................................................................................6
4.4 Solar Heating Panels .......................................................................................................................................7
4.5 Human Power .................................................................................................................................................7
4.6 Wind Power ....................................................................................................................................................8
5.1 Recommended Energy Source Arrangement .....................................................................................................8
5.2 Feed In ............................................................................................................................................................9
6.1 Back-up power generation .................................................................................................................................9
7.1 Energy Storage................................................................................................................................................. 10
7.2 Power Monitoring........................................................................................................................................ 11
8.1 Feasibility ......................................................................................................................................................... 11
9.1 References ....................................................................................................................................................... 12
Executive Summary
As a business proposition the off grid eco-gym is not feasible due to the high costs of power storage and
necessary equipment costs for renewable energy. With an on grid scheme there is only a need for payment of
energy usage by the given entity whereas renewables will have high initial costs as well as maintenance costs.
Therefore the money effectively earned back by not paying for energy requirements does not outweigh the
extensive capital required for renewable resources.
Page |2
1.1 Introduction
85.1% (RenewableUK, 2014) of the United Kingdom’s electricity production is through non-renewable sources
such as oil, gas and nuclear energy. At current rates of consumption it is estimated that we will not have enough
oil to meet our demands by 2040 (IME, n.d). Renewable energy sources are becoming more important than ever
and need to be taken up on both a global and commercial scale to insure our energy demands are met. For
changes to be made there must be an incentive, businesses must have to see that they can profit from renewable
sources to make them make the switch. The objective of this report is to come up with a recommended plan for
a fully off-grid eco-gym for a client and discuss its feasibility in the current market.
2.1 Brief
The Client requires that the gym has these features:







1500 members
25m indoor swimming pool
Modern cardiovascular ad resistance training machines
Fully heated and lit building
Changing rooms and hot showering facilities
Small Café serving snacks and hot drinks.
Must be fully self-sufficient with its power demands requiring nothing from the national grid
The following reports shows our findings on estimated power requirements for the gym and discusses what
currently viable renewable energy generation sources could be used to meet the demand but also be cost
efficient.
3.1 Eco gym energy consumption
Our gym has a number of energy hungry aspects which need to be considered so that we are able to come to a
relatively precise conclusion on the total energy usage so that we know how much energy is needed to up-keep
the system.
3.2 Swimming Pool
For a gym of our calibre the pool will without a doubt consume a large amount of energy. It will need certain
pieces of equipment such as a dehumidifier, pump, ventilation and heat pumps.
In order to calculate the energy consumption of the pool, a pool of a similar size was researched. Data from
SportEngland (2012) showed a pool which was the required size of four lanes and of twenty five metres. For
our gym we undertook a pool of this size as the membership was relatively low. The value of energy required
for a pool of this size was 186kWh/day.
Further, to calculate the total consumption of the entire pool it would require extensive knowledge of the
other pieces of equipment. Hence this required external research which proved useful after obtaining a
website by Sedac (2012) with the proportions of energy usage of an indoor pool in USA. After disregarding
cooling we produce a pie chart of including: pool heating, space heating, changing facilities, lighting,
dehumidification, pumps, other (café and reception) and ventilation. Using the value from earlier of
Page |3
186kWh/day this accounts for a total of
twenty seven percent this will give a total of
691kWh/day. As one of my team-member
had already calculated the energy required
for lighting and I have added the value for
space heating to the heating section hence
have removed these values from the total for
the pool as they will be included for the final
value. Total of energy is about 505kWh/day
which is equal to about 184MWh/year
Figure 1 Floor plan of Eco-Gym
Office and Reception 4x4m = 16m2
3.3 Lighting
In order to calculate the total power needed for lighting, we have divided the whole gym into two sections.
Section one encompasses the swimming pool and the cardio vascular area. Section two includes the rest. For
section one we had to use high bay lights due to the height of the swimming pool and cardio area. As for
section two we have use standard LED lights.
The numbers of light is given by the formula: (Student Notes, 2003)
𝑁=
Where,
N =
E =
A =
F =
UF=
MF=
dirt.




𝑁=
𝐸×𝐴
𝐹 × 𝑈𝐹 × 𝑀𝐹
number of lights needed.
light intensity required (lux)
area (m2)
average energy per unit time provided by each light (lm)
utilisation factor, an allowance for the light distribution of the luminaire and the room surfaces.
maintenance factor, an allowance for reduced light output because of deterioration and
The recommended luminance required for swimming pool and exercise area is 300 lux.
(Sport England, 2012)
Area = 360+400 = 760𝑚2
Each high bay light fitting’s performance and specifications: (Vivid LEDs, 2013)
120 watts, 10039 lumens, UF 0.7, MF 0.65.
300×760
10039×0.7×0.65
=50 lights
𝑇𝑜𝑡𝑎𝑙 𝑝𝑜𝑤𝑒𝑟 𝑓𝑜𝑟 ℎ𝑖𝑔ℎ 𝑏𝑎𝑦 𝑙𝑖𝑔ℎ𝑡𝑖𝑛𝑔𝑠 = 120 × 50 = 6𝐾𝑊

The recommended luminance required for office, reception and café is 250 lux. (The Engineering Toolbox,
ND)

Each spotlight light fitting’s performance and specifications: 6 Watts, 580 lumens, UF 0.5, MF 0.80.
(Light Rabbit, 2015)
Page |4
𝑁=
250×240
580×0.5×0.8
=259lights
𝑆𝑝𝑜𝑡𝑙𝑖𝑔ℎ𝑡𝑠 𝑙𝑖𝑔ℎ𝑡𝑖𝑛𝑔 𝑝𝑜𝑤𝑒𝑟 = 259 × 6 = 1.554𝐾𝑊
𝑇𝑜𝑡𝑎𝑙 𝑙𝑖𝑔ℎ𝑡𝑖𝑛𝑔 𝑝𝑜𝑤𝑒𝑟 = 6000 + 1554 = 7.554𝐾𝑊
𝐷𝑎𝑖𝑙𝑦 𝑐𝑜𝑛𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛

7554 × 16
= 120.9𝐾𝑊𝐻
1000
As the average day light in England is 12 hours, therefore, we have considered using large windows and
roof windows which will compensate 70% of the lightings. (Project Britain, 2013)
𝑇𝑜𝑡𝑎𝑙 𝑝𝑜𝑤𝑒𝑟 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 𝑓𝑜𝑟 𝑙𝑖𝑔ℎ𝑖𝑛𝑔𝑠 = 120.9 × 0.3 × 365 = 𝟏𝟑𝟐𝟒𝟎 𝑲𝑾𝑯 𝑷𝒆𝒓 𝒀𝒆𝒂𝒓
3.3 Heating
The average temperature in Bristol is 11°C (YR, 2014) and the minimum temperature required for the office,
reception, cafeteria and hallway is 21°C. (Seppänen, O et al, 2006)
The formula for heating is given by H = (kA / x) x (Tinternal – Texternal) where H is the heat, k is the thermal
conductivity, A is the area in meters cube, x is the width of insulation and T is the temperature. We have
considered the wall material to be foamed concrete as standard. (METBD 330, ND)



Foamed concrete has a thermal conductivity of 0.1 W/mK. (EAB Associates, ND)
Insulation has a standard thickness of 100mm. (Brinkley, M, 2011)
The total area for Office, reception and cafeteria including setting area is 160𝑚2 with the height of
2.5𝑚2 .
𝐻𝑜𝑓𝑓𝑖𝑐𝑒,𝑟𝑒𝑐𝑒𝑝𝑡𝑖𝑜𝑛 𝑎𝑛𝑑 𝑐𝑎𝑓𝑒𝑡𝑒𝑟𝑖𝑎 = (0.1 × (160 × 2.5)/0.1) × (21-11.3) =3880W
3880 × 16
× 365 = 22659𝐾𝑊𝑌
1000

We assume that the heating will be on 30% of the time.
22659 × 0.30 = 𝟔𝟕𝟗𝟕. 𝟕𝑲𝑾𝑯 𝑷𝒆𝒓 𝒀𝒆𝒂𝒓

The cardio vascular area has a dimension of 400𝑚2 and height of 4m. The minimum temperature
required is 16°C.
𝐻𝐶𝑎𝑟𝑑𝑖𝑜 𝑣𝑎𝑠𝑐𝑢𝑙𝑎𝑟 = (0.1 × (400 × 4)/0.1) × (16-11.3) =7520W
7520 × 16
× 365 = 43917𝐾𝑊𝑌
1000
43917 × 0.30 = 𝟏𝟑𝟏𝟕𝟓𝑲𝑾𝑯 𝑷𝒆𝒓 𝒀𝒆𝒂𝒓
𝐻𝑆𝑤𝑖𝑚𝑚𝑖𝑛𝑔 𝑃𝑜𝑜𝑙= 186 x 13/21 = 115 kWh per day
115kWh x 365 x15/24 = 26234KWh Per Year
Total heating power required = 6798 + 13175 + 26234 = 𝟒𝟔𝟐𝟎𝟕𝑲𝒘𝑯 𝑷𝒆𝒓 𝒀𝒆𝒂𝒓
Page |5
3.4 Air-conditioning
𝑇𝑜𝑡𝑎𝑙 𝐴𝑟𝑒𝑎𝐶𝑎𝑟𝑑𝑖𝑜 𝑣𝑎𝑠𝑐𝑢𝑙𝑎𝑟,𝑜𝑓𝑓𝑖𝑐𝑒,𝑟𝑒𝑐𝑒𝑝𝑡𝑖𝑜𝑛 𝑎𝑛𝑑 𝑐𝑎𝑓𝑒𝑡𝑒𝑟𝑖𝑎 𝑎𝑟𝑒𝑎 = 141𝑚2
Total BTU needed 68000, Cooling Output 20kW, Supply Airflow m3/h: 2960
We assume that the number of days that air conditioning will used per year is 189 days and it will be used 30%
of the time.
20000 × 16
× 124 = 39680𝐾𝑊𝑌
1000
𝑇𝑜𝑡𝑎𝑙 𝑝𝑜𝑤𝑒𝑟 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 𝑓𝑜𝑟 𝑎𝑖𝑟 𝑐𝑜𝑛𝑑𝑖𝑡𝑖𝑜𝑛𝑖𝑛𝑔 = 39680 × 0.30 = 𝟏𝟏𝟗𝟎𝟒𝑲𝑾𝑯 𝑷𝒆𝒓 𝒀𝒆𝒂𝒓
3.5 Miscellaneous
As shown above the heating, lighting, air-conditioning and swimming pool energy consumptions have all be
calculated. Other parts of the gym need to be taken into consideration such as the gym and café equipment.
Café (Hedrick, R, 2011)
Reception (Energy Usage Calculator, 2015)
Refrigeration - 35kwh/day
Two computers – 4.32kWh/day
Coffee machine/boiler - 11kwh/day
Printer – 0.0225kWh/day
Juicer - 9.5kWh/day
Phone – 0.048kWh/day
Total = 55.5kWh/day = 20258kWh per year
Total = 4.593 kWh/day = 1676kWh per year
3.6 Gym Equipment
Pieces of equipment that need to be taken into consideration are three rowing machines, six bikes, eight crosstrainers and eight treadmills.
As plenty of these machines can output a reasonable amount of power some of them can be used to produce
energy.




Three rowing machine can produce 0.6kWh and therefore 0.6x (15-5) = 6kWh/day. 15-5 was used as
the gym is open for 15 hours and we have assumed that each machine will only be used for two thirds
of the time. (University of Minnesota Duluth, n.d)
Six bikes can produce 1.92kWh and therefore 19.2kWh/day (Data taken from pedal-a-watt stationary
bike) (Life Fitness, 2010)
Eight treadmills will use 4kWh and therefore 40kWh/day. (Life Fitness, 2010)
Eight cross-trainers will use 0.8kWh and therefore 8kWh/day. (Life Fitness, 2010)
Hence the total amount of energy used will be 48kWh/day and the total amount produced will be
25.2kWh/day. Therefore the gym equipment will require 48-25.2=22.8kWh/day. This is 8322kWh/year.
3.7 Total Power Consumption
Adding up all the previous values we obtain a total power consumption of:
184,309 + 13,240 + 46,207 + 11,904 + 20,258 + 1,676 + 8,322 = 286MWh/year
Page |6
1%
Power
3%
7%
Swimming Pool
Lighting
Heating
Air-conditioning
Café
Reception
Gym Equipment
4%
16%
64%
5%
Figure 2 – Total Power Consumption of Gym
4.1 Possible Sources of Renewable Energy
The Bristol area has very good potential in renewably sourced energy due to its location in the UK. It is far south
enough to be in an area of high light intensity averaging at 137 Wm-2 (Met Office, 2014) throughout the year, as
well as being elevated enough to have a high average wind speed of 5.5 ms-1 (ESRU, 1999). Bristol is also situated
on the river Severn which is the largest river in the UK. The Severn is also unusually fast for its size travelling at
an average of 4.4ms-1(BBC, 2014). This collection of factors can all be exploited using varying methods of capture
as shown below.
4.2 Solar Cells
In the UK a 4kW system that is 28m-2 in size is expected to cost around £6000 at current prices (theecoexperts,
2015). This is the equivalent of 15-20Wm-2 at £215 per square metre. With total building area of 1000m2 once
can expect to be able to fit around 400m2 of solar arrays on the roof providing the benefits in Table 1.
Table 1 – Possible Power Output and Savings from a 400m2 Solar Array
Item
Power
Output
(W)
20.00
Cost (£)
Quantity
Total
Power
(kW)
8.00
kWh
year
per Total
Cost (£)
Savings per Payback
year (£)
Time (yr)
Solar
215.00
400.00
70,080.00
86,000.00 7,358.40
11.69
Cells
Solar Photovoltaic cells are often seen now as a very modern and realistic approach to renewable energy. They
have a 20 year lifetime and could pay for themselves within 12 years making them a viable option for the gym,
providing that there can be enough of them to provide and meaningful wattage.
4.3 Transparent Solar Cells
Transparent Solar Cells as explained by Anthony, S (2014) in the same way as traditional solar cells put have the
bonus of being transparent. This allows increased area in which to install them as they can be used in place of
glass windows. They work by absorbing light below the frequency of visible light but allowing visible light to pass
straight through. An example of a possible scenario is shown in Table 2.
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Table 2 – Possible Power Output and Savings from a 600m2 Transparent Solar Array
Item
Transparent
Solar Cells*
Power
Output
(W)
3.00
Cost
(£)
200
Quantity Total
Power
(kW)
600.00
1.80
kWh per Total Cost Savings
year
(£)
per year
(£)
15,768
120,000
1,655.64
Payback
Time
(yr)
72.48
Despite the ability for increased area and the opportunity to have lower lighting costs (sky lighting) the
technology is currently behind and is far too expensive for the cost to make it a feasible idea.
4.4 Solar Heating Panels
Like Photovoltaic (PV) Solar Panels, these use light to provide free energy. Unlike, PV cells these use the solar
energy to create heat instead of electricity. Cool water can be pumped in and be heated by the sun then pumped
out at a higher temperature. See Table 3 for a scenario.
Table 3 – Possible Hot Water Output and Savings from a 150m2 Solar Water Heating Panels
(WorcesterBoschGroup, 2015)
Item
Power
Cost (£)
Output
(W)
Solar 0.00317L
2,500
Water hot water
Heat
per
Panel second
Quantity
6.00
Total
Power
(kW)
0.01902L
hot water
per second
kWh
Total
per year Cost (£)
600000L 15,000
hot
water
per year
Savings per Payback
year (£)
Time
(yr)
5000
(≈ 3.00
50000kWh
to heat per
year
This 100m2 is enough to provide complete heating of an indoor 200m2 pool providing that it is covered at night
as well as the hot water needed for the facilities taps and showers all year round. It needs to be noted however
that these will occupy the same space as the PV Cells and a compromise will have to be met to enable their use.
4.5 Human Power
One of the main aspects of gyms is the cardio and resistance machines. In general, cardio machines run off the
grid, but more and more are starting to become self-sufficient. And current early prototypes of both
cardiovascular and resistance train machines are capable of outputting up to 200W (home-generator, 2014). into
for the use of the other gym facilities.
Table 4 – Possible Hot Water Output and Savings from Human Power
Item
Human
power
Power
Output
(W)
150.00
Cost (£)
Quantity
1,000.00
15.00
Total
Power
(kW)
2.25
kWh per Total
year
Cost (£)
13,140
15,000
Savings per Payback
year (£)
Time
(yr)
1,379.70
10.87
It is estimated that on average the equivalent use of machines would be a constant use of 15 machines. It is also
estimated that each machine will cost an additional £1000 more than the on-grid counterparts. Taking this into
account (as show in Table 4) shows that despite their reasonable payback time, they do not produce much
electricity throughout the year.
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4.6 Wind Power
As stated before Bristol has an average wind speed of 5.5m2 which opens up good possibilities for wind power.
The Gym will be situated in a city centre which means that full size turbines are out of the question leaving
smaller commercial wind turbines. An example of the power output of a Gaia-Wind 133-11kW (gaia-wind,2015)
is shown in Table 5.
Table 5 – Possible Hot Water Output and Savings using two Gaia-Wind 133-11kW wind turbines.
Item
Power
Output
(W)
2,000.00
Cost (£)
Quantity
Total
Power
(kW)
4.00
kWh per Total Cost Savings
year
(£)
per-year
(£)
35,040
100,000
3,679.20
Payback
Time
(yr)
27.18
Wind
50,000
2.00
Power
Although the turbine has quite a high power output for its size, it is also very expensive and has a very large
payback time. They could be put in quite a large array as they on have a diameter of 11m but because of the
large payback time, it is unlikely that it would every pay for itself before it would need to be replaced due to
wear.
5.1 Recommended Energy Source Arrangement
By far the most power possible can be produced by the river turbine. Clean Current (2015) manufacture one
model that has a blade diameter of 2.5 metres which produces a constant 30kW and another with a diameter of
1.8 which produces 16kW. They are both rated to produce this power with a river speed of 3ms 1. The River
Severn runs at 4.4ms1 so we are likely able to expect even more power.
To save power it is recommended to also install the Solar Heating Panels. The 150m 2 arrangement will provide
the hot water for all of the required facilities with an impressive 3 year payback time.
The recommended configuration is shown in Table 6.
Table 6 – Power Output and Savings of the Recommended Renewable Energy Configuration
Item
Power
Output (W)
Large
Turbine
Small
Turbine
Solar
Water Heat
Panel
30000
Cost
(£)
250,0
00
16000
180,0
00
0.00317L
15,00
hot water 0
per second
Quantity
Total
Power (kW
kWh
per year
Total Cost (£)
Payback
Time (yr)
1
30
262800
250,000
9.06
1
16
140160
180,000
12.2
6.00
0.01902L
600000L
15,000
hot water hot
per second water/year
3
This has an estimated total installation cost of £445,000 and can produce at least 403,000kWh/y, which is an
29% overhead over the 286,000kWh/y required. The overhead is needed to help cope with possible maintenance
requirements of one turbine if it fails and not having the smaller one would result in only having a 20% overhead
which is very risky in an off grid system.
The river turbines have been shown to be safe for wildlife with study’s showing that fish tend to avoid them as
they can detect a disturbance in the water. Planning permission would need to be considered and local
Page |9
government would need to be contacted to allow construction. The turbines are installed deep in the water and
have a small footprint meaning that there would be little to no disturbance to normal river function.
5.2 Feed In
To help justify the massive overhead when not in use it is suggested to feed it back into the national grid. At
current rates, the UK government pays 12p per kWh (European Solutions, 2010). With an excess of 117MWh/y
this could produce an additional source of income of up to £14,040 per year.
6.1 Back-up power generation
Despite the inclusion of multiple reliable power generation and storage technologies, it is also necessary to
include a standby power source in the event of failure of a hydro-turbine or an energy shortage from the
lead/acid batteries. Initially, multiple forms of backup power supply were considered and compared based on
installation costs, size, running costs and power output. In order to comfortably meet the power demands of the
gym as a stand-alone back up device, it is recommended that a device with a rated output of 100kW is chosen.
Due to a desire to minimise greenhouse gas emissions from our generator of choice, fuel cells were considered.
A major advantage of this standby technology is the emission of only water vapour as a waste product; thus
eliminating the need for a separate storage area, and allowing for onsite location of the fuel cell unit.
Furthermore, the replacement of a combustion based generation method with fuel cells minimises the moving
parts required and therefore increases reliability. However, fuel cells for commercial use have only recently been
introduced to the market, and correspondingly, purchase and installation costs for a device large enough to meet
the demands of an off grid gym are high. In fact, fuel cell standby systems are at the stage of market life where
reliable purchase costs are difficult to find. A reasonable estimate based on GreenLight Innovation’s (a US fuel
cell manufacturer) current commercial fuel cells puts a 100kW fuel cell in the range of £380,000 to install, with
the running cost per kWh three times as high as a similarly sized diesel generator (PEM Solutions, 2013); clearly
financially unfeasible for a small commercial user.
A similar issue was met whilst considering a standby measure incorporating flywheel energy storage linked to a
battery bank. Although FES demonstrates a favourable efficiency of 80%, it sacrifices low cost as expensive
magnetic materials and alloys for bearings along with carbon fibre blade designs push up manufacturing costs.
Currently, the most affordable commercially available flywheel claims that an investment of £1,333 will output
1kW (Nelder, C, 2014), thus putting a theoretical 100kW device at £133,300; again far too large a sum for a small
commercial business.
The most sensible stand-by storage device given current technical advances and prices is still a generator that
relies on internal combustion. The eventual choice, Generac’s Commercial Series 100kW standby generator,
costs £15,650 to install (Generac, 2015); a far more sensible figure for this purpose. Furthermore, the generator
runs on natural gas which gives a few key advantages. Natural gas is a cleaner burning fossil fuel as compared to
diesel, thus maintaining the image of an eco-friendly setup. Natural gas will already be piped to the location
through the UK gas network, eliminating and need for storage and also ensuring that when required, the
generator can immediately begin to power the gym as natural gases can remain piped for long periods without
any decrease in quality. The final major advantage of natural gas is that, despite being slightly less energy dense,
it is a cheaper source compared to diesel. Early 2015 fuel prices indicate that diesel costs around £2.45 per gallon,
and the gasoline gallon equivalent of natural gas is around £1.40 (World Dept. of Energy, 2015). The combination
of a low installation cost, low running cost and a power output that comfortably covers the demands of the whole
gym place the natural gas generator as the main recommendation for a standby power system.
P a g e | 10
Table 7 - A comparison of the equipment investment required per kW produced by standby methods
Backup Power Source
NiCd batteries
Fuel Cells
FES
Natural gas Generator
Investment per kW (£)
£3450
£3875
£1333
£157
7.1 Energy Storage
Energy storage is essential to enable the gym to cope with power fluctuations which will occur due to the volatile
nature of the power output from renewable sources especially solar power. A storage system will create a
balance between power supply and demand instantaneously. Storage is also needed during periods of power
outages and in case of emergencies. Our estimated peak power output is 63kW which exceeds our total power
generation; therefore an energy storage system is vital to keep the gym running during this peak period. There
are many different ways of storing energy (Energystorage.org.uk, 2015):





Chemical Energy storage
Electrochemical storage
Electrical storage
Thermal storage
Mechanical storage
We firstly considered using a flywheel, which stores electricity as kinetic energy. An electrical input causes a rotor
to spin in an almost frictionless enclosure, which gives an efficiency of 80%. When short term back up is needed
because power generation fluctuates, the inertia allows the rotor to continue spinning and this kinetic energy is
converted to electricity (Energystorage.org, 2015).The advantages of using a flywheel for energy storages are
that they’re low maintenance, whilst having a long life and small environmental impact, this will help reduce the
costs of our gym. There are many disadvantages however; a flywheel that would be capable of storing our
required power would need to be very large, which is not ideal in a city location. Also due to the large stresses
and strains that are present when the rotor spins, there is a limit on how fast they can go before fracturing. The
amount of energy that can be stored is proportional to the object’s moment of inertia times the square of its
angular velocity. Due to the large size of flywheel that would be needed to provide the required power of 63kW
for our gym, we have discounted the use of a flywheel.
Hydrogen storage was another storage method we considered. During this process electricity can be converted
to hydrogen via electrolysis, this hydrogen can be stored in pressurised vessels for prolonged periods of time and
re-electrified via combustion or in fuel cells (Energystorage.org, 2015). Hydrogen energy storage uses relatively
new technologies and therefore has a low efficiency of 50-60% in comparison to other methods. This is a very
expensive storage method, because the process of creating hydrogen uses new technologies which are still
advancing, therefore it is not feasible to use within our gym.
We chose to use batteries (electrochemical storage) as our method of energy storage due to their high efficiency,
low cost and low maintenance in comparison with the other storage methods. We decided to use lead-acid
batteries after doing a comparison to lithium-ion batteries, this is majorly due to a lead-acid battery being much
more economical at £293,000 compared to a lithium-ion battery that costs £650,000 (BatteryUniversity, 2015).
We found that lithium-ion batteries have a higher energy density than lead-acid, as well as a higher life span, up
to 5000 cycles from a lithium-ion battery compared to 2000 from a lead-acid battery. A Lithium-ion battery is
P a g e | 11
able to charge at 100% efficiency whilst a lead-acid one can only charge at 85% efficiency (PowerTech Systems,
2015). Although the lithium-ion battery seems much more desirable, we will use a lead-acid battery in our gym,
this is because the lead-acid battery is under half the cost of a lithium-ion battery, massively reducing our setup
costs, increasing the feasibility of our off-grid gym.
7.2 Power Monitoring
A power monitoring system involves a level of meters connected to the internet to provide real time data on
the energy system within our gym. The meter has large storage capacity and continually monitors the power,
allowing a positive approach to energy management (Hoveyelectric.com, 2015). A power monitoring system is
needed in our gym to maximise the fuel efficiency by using battery as an energy buffer, meaning the generator
is only used when required to recharge batteries, or when the loads are particularly high. Allowing the
generator to run for as little time as possible at maximum load, keeping its efficiency at the optimum.
We have found a system called Eplex which is a control system that uses an iPad interface that mimics
information and controls that happen within the generator, battery, and fuel sources this can display fuel
levels, battery state of charge, renewable energy entering the system as well as generator loading (Energysolutions.co.uk, 2015).
8.1 Feasibility
In order to find out whether the construction of an eco-gym would be feasible in the long-term we looked into
the total costs of off-grid installation and maintenance. We looked at the life of our renewable power generators
and assumed that they will have on average a life span of twenty years with batteries having a lower life span of
ten years. Therefore we had to consider a battery replacement after ten years.
The total cost for initial installation and battery replacement would be equal to £1,037,000 for the period of
twenty years. As we feed back some power into the grid we make a small profit of £280,800 which will reduce
our total cost to £756,200.
On the other hand if we ran the gym using the grid we would pay an average tariff as suggested by Kingspan
Energy (2013) of 14p per kWh which will cost £801,000 over a period of twenty years.
Which means that we can make a total saving of £44,800, realistically extra costs will be incurred if a generator
fails and needs to be replaced or minor replacements of photovoltaic cells.
If the client were to invest the initial capital to a bank and with an average interest rate found from
MoneySuperMarket.com (2015) of three percent he or she would make £574,000 due to compound interest.
Comparing this profit to the potential income from renewable sources this would be eighteen times greater,
therefore, an off-grid system would not be financially feasible due to the high cost of power storage. Despite
this, with technological advances the costs of power storage systems will decrease in the future making a selfsufficient off-grid gym a realistic venture.
P a g e | 12
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